Abstract
In a precueing task, observers must detect a signal appearing at one of several locations, with a precue indicating the most likely signal location. Typically, valid precues (indicating the correct signal location) lead to better performance than invalid precues. While cueing effects have been interpreted as evidence of a limited capacity attentional mechanism (e.g., Posner, 1980), several authors note that the task suffers from the problem of structural uncertainty (Sperling & Dosher, 1986; Kinchla, et al., 1995; Shiu & Pashler, 1995). In particular, an ideal observer also predicts a cueing effect, calling into question the role of limited capacity in this task (Eckstein, et al., 2002).
The precueing task can be supplemented with 100% valid postcues, thereby removing structural uncertainty. Several studies still found precueing effects with 100% valid postcues (e.g., Dosher & Lu, 2000; Luck, et al., 1996; Hawkins, et al., 1990), appearing to strengthen the argument for a limited capacity attentional mechanism operating at the (post)cued location. However, this argument depends upon the assumption that humans also act without structural uncertainty. To assess this question, we measured classification images for a precueing task with 100% valid postcues. Observers performed a contrast discrimination of Gaussian blobs (sd = 8.3min) in image noise (sd = 11.7% contrast) at 4 or 8 locations, with a precue validity of 62.5%. Observers nearly always correctly localized the postcue, and localization was not hindered by invalid precues. Despite this, we found that some observers had substantial classification images at the invalidly precued location (‘attentional leaking’), indicating that these observers were using information from that location. These results suggest that precueing effects with 100% valid postcues may not completely reflect limited capacity attentional changes at the postcued location, and instead may reflect observers acting with structural uncertainty in a task without structural uncertainty.
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